Problem: A tank is to be filled with water. When the tank is one-sixth full, 130 gallons of water are added, making the tank three-fifths full. How many gallons does the tank contain when it is completely full?
Solution: The difference between three-fifths full and one-sixth full is $\frac{3}{5}-\frac{1}{6}=\frac{13}{30}$ of the tank's capacity.  Let $x$ be the capacity of the tank in gallons.  Since $\frac{13}{30}$ of the tank's capacity is 130 gallons, we have $\frac{13}{30}x = 130$.  Multiplying both sides by $\frac{30}{13}$ gives $x = 300$, so the capacity is $\boxed{300}$ gallons.